Electrical connectors and method of making same

ABSTRACT

An electrical connector for subsurface use under conditions of high temperature and pressure, said connector, comprising a male member and female member, said male member employing a sealing annulus disposed between adjacent refractory sleeves, the annulus being bonded to the metal jacket of the male member, to the refractory sleeves and to the conductive pin.

United States Patent Ring et al.

[ Feb. 19, 1974 ELECTRICAL CONNECTORS AND METHOD OF MAKING SAMEInventors: Sandiford Ring; Russell K. Ring,

both of P.O. Box 14666, Houston, Tex. 77021 Filed: May 1, 1972 Appl.No.: 249,359

References Cited UNITED STATES PATENTS 1/1973 Swehla 339/60 C 4 M y Y 15o 5 52 55 551 50 66' 65 54 7622 29 FOREIGN PATENTS OR APPLICATIONS1,111,347 4/1968 Great Britain 339/61 R Attorney, Agent, or F irm RalphR BrowriiTigTC James Bushman ABSTRACT An electrical connector forsubsurface use under conditions of high temperature and pressure, saidconnector, comprising a male member and female member, said male memberemploying a sealing annulus disposed between adjacent refractorysleeves, the annulus being bonded to the metal jacket of the malemember, to the refractory sleeves and to the conductive pin.

13 Claims, 6 Drawing Figures f 5a a 70 62 68 26 14 I Mb 29 ELECTRICALCONNECTORS AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION 1.Field of the Invention The present invention relates to electricalconnectors for use in adverse environments and particularly for use inconnecting wires to underground and/or underwater instruments so thatelectrical signals can be relayed to the surface. Such equipment is usedin seismic exploration such as for example in searching for oil andother minerals. Prior to about 1965, drilling for oil was limited todepths of approximately 20,000 feet. At these depths, temperaturesseldom exceeded 400 F. More recently, however, drilling to depths inexcess of 20,000 feet has become common. At these greater depthstemperatures often exceed 500 F. These adverse temperature conditionsare encountered not only in oil exploration drilling but are found aswell in wells used to monitor underground nuclear explosions and inother applications. Moreover, in underwater exploration, connectorscapable of withstanding high pressures are absolutely necessary.

2. Description of the Prior Art A typical connector of the type to whichthe invention pertains includes a male member and female member. Thefemale member comprises a lead wire in contact with a conductive elementwhich is generally surrounded by a sheath of elastomeric material. Themale member comprises a conductive pin, the central portion of which iscovered by an insulating material which in turn is encased in a metaljacket. One end of the pin engages the conductive element in the femalemember and the other end extends into the instrument housing.

Connectors of the type described which may be satisfactory at depths of20,000 feet or less and temperatures of 400 F or less, present problemsif used at greater depths and higher temperatures. One problem is thatthe organic based insulators such as the elastomeric sheaths of thewires and female members become carbonized and useless at temperaturesin excess of about 400 F.

* A second, more severe problem involves the male member. It has beenrecognized that ceramics of suitable refractory materials which canwithstand high temperatures, might be useful as insulating materials,for example between the pins and the metal jackets of the male members.However, if the coefficient of thermal expansion of a metallic part,e.g., the jacket, of such a male member is not compatible with that ofthe ceramic or refractory portion, the ceramic may crack at hightemperatures as it and the jacket expand atdifferent rates. Thus, whereceramics made from refractory materials have been used heretofore asinsulators in the male members of such connectors it has been necessaryeither to leave the ceramic and metal parts unfused and therefore notleakproof or, where the metal and ceramic parts were fused to render themember leakproofl-to choose metals and ceramics having compatiblecoefficients of thermal expansion. This severely limits the types ofmaterials which may be used. Furthermore, the metals which arecompatible with the ceramics are often unsuitable for underground orunderwater use because of corrosion problems posed by the alkalies andacids found in subsurface environments.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide an electrical connector having fused metallic andceramic components whose coefficients of thermal expansion are notnecessarily compatible.

It is a further object of the present invention to provide connectors inwhich a greater variety of metals may be used in fused combinations withceramic insulators.

Another object of the present invention is to provide a method formaking an improved male member for an electrical connector.

It is a further object of the present invention to provide a male memberfor an electrical connector having an annulus of sealing glasssurrounding the pin between a pair of refractory converings and bondedto the refractory coverings, to the pin, and to a metallic jacket.

Still another object of the present invention is to provide a femalemember for an electrical connector having an outer elastomeric sheathand a temperature resistant inner polymeric sheath with means forsealing between said inner sheath and the male member.

In a connector according to the present invention the male membercomprises a conductive pin, a portion of which is circumferentiallyembraced by a sealing annulus comprised of compression glass. Portionsof the pin adjacent the annulus are circumferentially surrounded byrefractory coverings or sleeves which are bonded to the glass annulusand fused to the pin, the annulus being bonded to the pin as well.

A jacket of metal circumferentially surrounds the annulus and thoseportions of the refractory coverings which are directly adjacent theannulus. During production the jacket is caused to shrink around therefractory coverings and the glass annulus and is bonded to the glassannulus and fused to the refractory covering. The seals formed betweenthe glass annulus and adjacent surfaces of the refractory coverings, pinand jacket cooperate with other features of the connector to preventleakage from the high pressure area outside the connector to the lowpressure area in the instrument housing.

In one form of the invention, when the metal jacket has a thermalcoefficient of expansion incompatible with that of the compression glassusually employed to form the annulus, the glass sealing annulus iscomprised of two components an inner core of the compression glass andan outer, relatively thin coating of a glass having thermoplasticproperties compared to the inner core and located between the core andthe jacket.

In another form of the invention, when the glass sealing annulus iscomprised primarily of a compression glass having a thermal coefficientof expansion incompatible with that of the refractory coverings,relatively thin sections of a glass which is thermoplastic as comparedwith the compression glass, are disposed between the abutting surfacesof the refractory coverings and the compression glass core.

Thus it will be seen, that under certain circumstances, the glasssealing annulus will comprise a twocomponent system, a compression glassand a glass which has thermoplastic properties as compared with thecompression glass.

In a preferred form of the invention, the female member includes twoprotective insulating sheaths: an outer sheath of elastomeric materialand an inner sheath of a heat-resistant polymeric material such aspolytetrafluoroethylene. The elastomeric sheath seals around the malemember at low temperatures and the polymeric sheath seals around themale member at higher temperatures at which the elastomer is destroyedor rendered useless. The inner surface of the heat resistant polymericsheath is provided with an annular groove, and the Corresponding part ofthe male member with a mating annular ridge such that when the male andfemale members are connected. positive scaling is effected between thepolymeric sheath and the jacket on the male member.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fullyexplained by the following detailed description of a preferredembodiment and by the drawings wherein:

FIG. 1 is a longitudinal cross-section of a connector and a portion ofan instrument housing, with several parts of theconnector being shown inelevation;

FIG. 2 is a'transverse cross-section of the male member along lines 2-2of FIG. 1;

FIG. 3 is a transverse cross-section of the female member with the malemember engaged therein along lines 3-3 of FIG. 1;

FIG. 4 is a transverse cross-section of the female member taken in thesame plane as FIG. 3 but without the male member engaged in the femalemember;

FIG. 5 is an enlarged section through a portion of a male memberillustrating one form of glass sealing annulus; and

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, it can beseen that the electrical connector indicated generally by the letter Ccomprises a male member M and a female member F. The male membercomprises a central elongate pin 2 of a conductive metal such as a 52percent nickel alloy or Kovar. The pin 2, usually of circularcross-section, has an enlarged diameter part 6. The end 8 of smallerdiameter part 4 is adapted for engagement in the female member F whilethe end 10 of larger diameter part 6 is designed to be disposed in aninstrument housing I. End 10 may be provided with male thread 92 forsuitable connection to an instrument within housing I.

Part 4 of pin 2 is circumferentially surrounded by a sealing annulus 12comprised of a material such as borosilicate glass, potash-soda-bariumglass or some other such glass of high compressive strength (hereincalled compression glass"). On either side of the annulus 12 are tubularcoverings or sleeves 14 and 16 preferably of a ceramic formed from asuitable refractory such as aluminum oxide, zirconium oxide, acombination of aluminum and silicon oxides, a combination of aluminumand magnesium silicates, etc. Covering 14 is disposed between end 8 ofpin 2 and annulus l2, and is bonded to annulus 12 at surface 18 whilecovering 16 is disposed between annulus 12 and the larger diameter part6 of pin 2 and is bonded to annulus 12 at surface 20.

A metallic jacket 22 circumferentially surrounds the annulus 12 and atleast those portions of the coverings l4 and 16 which are closest toannulus 12. In the particular connector shown, the jacket 22 surroundsthe entire length of covering 16 and extends longitudinally beyond ittoward end 10 of the pin 2. The jacket 22 is bonded to annulus 12 atsurface 24 in a manner to be described below. When used in a corrosiveenvironment, jacket 22 is preferably formed of a non-corrosive metal.For example, a 300 series stainless steel might be used. Any number ofother non-corrosive metals such as stainless steel alloys and othermetallic alloys may be used.

The jacket 22 has a part 26 usually of annular crosssection which isadapted for engagement in the female member F and a part 28 which isadapted for engagement in the instrument housing I. As best seen in FIG.2, between parts 26 and 28 is an enlarged polygonal section 27 withouter surfaces 29 adapted to be gripped in screwing the male member intoinstrument housing I. Ceramic covering 14 has a portion 14a whichextends longitudinally beyond part 26 toward end 8 of the pin 2. Portion14a of ceramic covering 14 and part 26 of jacket 22 are of substantiallyuniform outer diameter with the exception of an annular ridge or dogknot 32 projecting circumferentially from part 26. The remaining portion14b of ceramic covering 14 has an outer diameter which is substantiallythe same as that of the glass annulus l2 and the larger diameter part 6of pin 2. The portion 16a of ceramic covering 16 which is closest topart 6 of pin 2 is also of substantially the same outer diameter asportion 14b of covering 14, part 6 of pin 2, and annulus 12. Portion16b, closest to annulus 12 is of a smaller outer diameter than portion160. Tubular coating 30 of insulating glass surrounds portion 16a and aportion of part 6 between portion 16a and end 34 ofjacket 22. The innersurface 36 ofjacket 22 is configured to fit closely along the adjacentouter surfaces of the various glass and ceramic elements 14, 12, 16 and30.

Part 28 of jacket 22 comprises a smooth portion 28a of substantiallygreater outer diameter than that of part 26, and another portion 28b ofslightly smaller outer diameter and having a male thread 38. Aresilient, O- ring gasket 40 extends circumferentially of part 28 in anannular groove 42 in portion 28a. An annular metal gasket 44 extendscircumferentially of part 28 at the intersection of parts 28a and 28b.Housing I has a bore 46 threaded at 48 to engage male thread 38 andallow for connection between housing I and male member M of connector C.Bore 46 is configured such that sealing between housing I and part 28 iseffected by gaskets 40 and 44.

The female member F of the connector C comprises an inner heat-resistantpolymeric sheath 50. Sheath 50 should be somewhat resilient and ispreferably formed by polytetrafluoroethylene or some other fluorocarbonresin. Sheath 50 has a longitudinal bore 52 therein.

Within bore 52 and distal the mouth 54 of said bore is a rigid sleeve 56which may be formed, for instance, of brass. Disposed within sleeve 56is an electrically conductive element comprising a slotted spring 58which may be of a beryllium-copper alloy or the like. A shoulder 84 inthe interior of sheath 50 abuts sleeve 56 and spring 58. Spring 58comprises a rigid part 58a and a lip member 58b which is biased towardpart 58:1 (See FIG. 4) and deflectable radially outwardly, part 58a andlip 58b being separated by a slot 60. The extension 66.0f part 58a whichis located between the end 62 of lip 58b and the mouth 54 of bore 52 hasan annular opening 68 therethrough which is continuous with an arcuatelongitudinal groove 70 in part 58a. An arcuate groove 72 in lip 58b islocated opposite groove 70 in part 58a and aligned with opening 68.

An outer sheath 74 of an elastomer such as synthetic or natural rubber,polyethylene, ethylene-propylene rubber, etc. Surrounds the exterior ofthe inner heatresistant sheath 50. Sheath 74 has an annular opening 76aligned with the mouth 54 of bore 52. A conductive lead wire 78 extendsthrough the sheaths into the element 58 and is soldered to element 58.Wire 78 has two protective insulating coatings: an inner coating 80 ofpolytetrafluoroethylene or some other insulating material capable ofwithstanding high temperatures, and an outer coating 82 of an elastomersimilar to that of sheath 74. The coating 80 also extends through thetwo sheaths 50 and 74 up to the point where the wire 78 is soldered tospring 58.

The inner diameter of the bore 52 in sheath 50 and the aligned opening76 in sheath 74 are sized so that part 26 ofjacket 22 and portion 14aofceramic convering 14 fit snugly therein. Inner sheath 50 is providedwith an annular groove 85 positioned so as to be aligned with ridge 32when ceramic portion 14a is abutting cylinder 56 and element 58. Theresiliency of the sheaths 74 and 50 allows ridge 32 to snap into groove85 when the male and female members are joined.

In fabricating the male member, the variations in inner and outerdiameters of the various parts, described above, form shoulders whichaid in assembling the parts. Refractory covering 16 may be placed on pin2 from end 8 so that it abuts larger diameter part 6 of the pin 2.Insulating glass 3 may then be placed within part 28b ofjacket 22 andthis unit may be placed on the pin 2 from end 8 so that shoulder 86abuts portion 16a of refractory covering 16 and shoulder 88 of covering14 abuts jacket 22.

After the parts have been assembled, jacket 22 is selectively heated andthen cooled so that its shrinks around the ceramic and glass parts. In apreferred method of constructing the male member M, male member M isplaced in an induction furnace. Being metallic and conductive, thejacket 22 will heat at a faster rate than the insulating glass, sealingglass annulus, and

. ceramic coverings. Depending on the materials employed, male member Mis heated to the desired temperature and then cooled to a lowertemperature over a relatively short period of time. The jacket is keptat the lower temperature for a period of time sufficient to allowannealing of the-glass in annulus 12 and then further cooled to ambienttemperature. The temperatures and times of heating and cooling will varydepending on the materials used. The cooling is preferably done in anatmosphere of argon, nitrogen or some other inert gas to preventoxidation of the metal portion of the connector. The cooling andsimultaneous shrinking of the jacket causes the various elements to fitso tightly together that jacket 22 is in effect bonded or fused to theceramic coverings. The shrinking also fuses or bonds layer 30 ofinsulating glass to pin 2 and jacket 22 so that pin 2 is prevented fromrotating by torque when a connection is made to thread 92.

The heating, followed by the cooling and shrinking, bonds the glassannulus 12 to the pin 2, jacket 22 and ceramic coverings 14 and 16 alongrespective surfaces 90, 24, 18 and 20. The bonds between the variouscomponents are believed to be chemical bonds as well as physical seals,the latter being due to the tight engagement caused by shrinking, or acombination of the two.

The maintenance of the fluid tight seals formed at surfaces 90, 24, 18,and 20 may be insured in several ways. In one form of the invention theglass annulus 12 has a thermal coefficient of expansion compatible withthat of the jacket 22. Thus the two expand and contract in acomplementary manner such that the annulus 12 is never cracked byexpansion of either member yet the two remain pressed togethersufficiently tightly to form effective seals along the surfaces of theannulus 12. Metals whose thermal coefficients of expansion arecompatible with compression glasses are often of the non-corrosive type,c.g., stainless steel and stainless steel alloys, whereas metalscompatible with refractories are usually corrosive or otherwiseunsuitable for underground use because of weak physical properties,unavailability or magnetic susceptibility. It should be understood thatthe term compatible as applied to the thermal coefficients of expansionof the various materials does not necessarily mean identical thermalcoefficients of expansion but rather coefficients so related that thevarious parts expand and contract when subjected to varying temperaturesat a rate which ensures the integrity of the connector will bemaintained.

In FIG. 5 is shown a form of the invention wherein the metal jacket hasa thermal coefficient of expansion incompatible with the compressibleglass generally employed in forming annulus 12. In the embodiment inFIG. 5, annulus 12 comprises a core 120 of borosilicate glass,potash-soda-barium glass or some other such compression glass and arelatively thin outer peripheral coating 12c disposed between core 12aand jacket 22 of a glass having thermoplastic properties relative tocore 12a. For example, a suitable glass to be used as outer covering 120is a glass such as silicate glass, borate glass, borosilicate glass,etc. containing relatively large amounts of lead oxide or an oxide ofsome other heavy metal. A typical high lead silicate glass usable as thethermpolastic coating has a composition comprising (by weight)approximately 72 percent PbO, l4% B 0 and 14% S0 Other glasses havingthermoplastic properties relative to the compression glass used may alsobe employed.

In FIG. 6 is shown still a further embodiment wherein the ceramiccovering 14 and 16 have thermal coefficients of expansion incompatiblewith core 12a of annulus 12. In the embodiment of FIG. 6, annulus 12comprises a central annular core 12a of a compression glass such asthose mentioned above and annular end sections 12b and 12d of a glasshaving thermoplastic properties relative to the core 12a. As noted abovefor the embodiment of FIG. 5, the relatively thin thermoplastic layers12b and 12d canbe comprised of a high lead silicate glass or some othersuch material. It should be unmoplastic glass which in turn is bonded tothe jacket or to the refractory sections or to all three if thecompression glass core is incapsulated in a thermoplastic glasscovering.

Other modifications of the connector disclosed herein might include theprovision in the annulus 12 of a layer of thermoplastic glass material(not shown) disposed to lie adjacent the pin 2.

It will thus be appreciated that connectors according to the inventionprovide a plurality of means for preventing leakage from the highpressure area H outside the connector to the low pressure area L in theinstrument housing I as well as other advantages. At low pressures, theouter sheath 74 of the female member seals against part 26 of jacket 22to prevent leakage between the male and female members. At hightemperatures, above 400F., the outer sheath 74 deteriorates and does notact as an effective seal. At the higher temperatures and pressures theinner sheath 74 complements the inner sheath 50 which often cannot actas an effective seal at low pressures. The sealing properties of thepolymeric inner sheath 50 are enhanced by the groove 85 and mating ridge32. The brass sleeve 56 prevents extrusion of material from the sheaths50 and 74 into the slit 60 which is'a problem at any pressure.Similarly, gasket 40 prevents leakage between the housing I and part 28at low temperatures while gasket 44 prevents such leakage at hightemperatures and pressures.

If for any reason fluid should leak between the male and female members,it is inhibited from further leakage between the elements of the malemember and into the housing by the tightness with which the elements ofthe male member are fused together. The glass annulus 12, beingcomprised of a glass of high compressive strength, helps to protect theceramic insulating coverings l4 and 16 from being crushed by expansionof the jacket 22. If ceramic covering 14 should crack, or if for anyother reason leakage should occur through the male member from the leadend in the female member, this leakage will be stopped by the sealsformed at annulus l2 and will not proceed into the instrument housing.The use of the relativelysmall annulus 12 thus allows the useofpreferredceramic coverings as insulators throughout the major portion of the malemember in a fused combination in which the thermal coefficient ofexpansion of the ceramic covering is not necessarily compatible withthat of the metal jacket. As noted above, the pin 2 may be made of anickel alloy or other metal compatible with ceramic in order to furtherenhance the salient characteristics of the connector.

The invention having been thus described, what is claimed is:

1. An electrical connector comprising a male memher, and a femalemember, said male and female members being releasably connectable to oneanother, said male member comprising a conductive pin having a first endand a second end, a glass sealing annulus circumferentially surroundinga portion of said pin intermediate the ends of said pin, a firstrefractory covering adjacent said annulus and circumferentiallysurrounding a portion of said pin between said first end and saidannulus, a second refractory covering adjacent said annulus andcircumferentially surrounding a portion of said pin between the annulusand said second end of said pin, and a metallic jacket circumferentiallysur rounding said annulus and portions of said refractory coveringsdirectly adajacent said annulus, said annulus being bonded to saidjacket, to said pin and to said refractory coverings.

2. An electrical connector according to claim 1 wherein said annulus iscomprised of a compression glass.

3. An electrical connector according to claim 1 wherein said annulus hasa thermal coefficient of expansion compatible with the thermalcoefficient of expansion of said jacket.

4. An electrical connector according to claim 1 wherein said annuluscomprises an inner core ofa compression glass and a relatively thinlayer of a glass having thermoplastic properties compared to said core,said layer being disposed between said core and said jacket.

5. An electrical connector according to claim 1 wherein said annuluscomprises a central core of a compression glass and opposing endsections of a glass having thermoplastic properties compared to saidcore, each of said end sections being thin relative to said core andbeing disposed between said core and one of said refractory coverings.

6. An electrical connector according to claim 1 wherein said jacket hasa portion extending longitudinally beyond said second refractorycovering toward said second end of said pin and wherein a tubularinsulating member is disposed between said pin and said extendingportion of said jacket.

7. An electrical connector according to claim 6 wherein said male memberfurther comprises gasket means disposed circumferentially of saidextending portion of said jacket for sealing between said extendingportion and an instrument.

8. An electrical connector according to claim 1 wherein said femalemember comprises a resilient, heat-resistant polymeric inner sheathhaving a bore for receiving said male member, an elastomeric outersheath surrounding said inner sheath and having an annular openingaligned with the mouth of said bore, a conductive element extendingthrough said sheaths, means disposed in said inner sheath for releasablyengaging said first end of said pin and means providing electricalcontact between said pin and said conductive element.

9. An electrical connector according to claim 8 wherein said jacket hasa part snugly receivable in said bore and said opening in said outersheath and has an annular ridge extending circumferentially thereaboutand said inner sheath has an internal annular groove in said borewhereby said ridge snaps into said groove when said male and femalemembers are connected.

10. An electrical connector according to claim 8 wherein said femalemember further includes a rigid sleeve disposed in said bore, and saidmeans for releasably engaging said pin and said means providingelectrical contact comprises a conductive spring in contact with saidconductive element.

11. An electrical connector according to claim 7 wherein said innersheath is comprised of a fluorocarbon resin.

12. An electrical connector according to claim 7 wherein said conductiveelement comprises a wire and an inner, insulating heat-resistantpolymeric coating is disposed around said wire and an outer protectiveelastomeric coating is disposed around said inner coating.

13. An electrical connector according to claim 1 wherein said pin has athermal coefficient of expansion compatible with the thermal coefficientof expansion of said refractory coverings.

II! i =8 4K

1. An electrical connector comprising a male member, and a femalemember, said male and female members being releasably connectable to oneanother, said male member comprising a conductive pin having a first endand a second end, a glass sealing annulus circumferentially surroundinga portion of said pin intermediate the ends of said pin, a firstrefractory covering adjacent said annulus and circumferentiallysurrounding a portion of said pin between said first end and saidannulus, a second refractory covering adjacent said annulus andcircumferentially surrounding a portion of said pin between the annulusand said second end of said pin, and a metallic jacket circumferentiallysurrounding said annulus and portions of said refractory coveringsdirectly adjacent said annulus, said annulus being bonded to saidjacket, to said pin and to said refractory coverings.
 2. An electricalconnector according to claim 1 wherein said annulus is comprised of acompression glass.
 3. An electrical connector according to claim 1wherein said annulus has a thermal coefficient of expansion compatiblewith the thermal coefficient of expansion of said jacket.
 4. Anelectrical connector according to claim 1 wherein said annulus comprisesan inner core of a compression glass and a relatively thin layer of aglass having thermoplastic properties compared to said core, said layerbeing disposed between said core and said jacket.
 5. An electricalconnector according to claim 1 wherein said annulus comprises a centralcore of a compression glass and opposing end sections of a glass havingthermoplastic properties compared to said core, each of said endsections being thin relative to said core and being disposed betweensaid core and one of said refractory coverings.
 6. An electricalconnector according to claim 1 wherein said jacket has a portionextending longitudinally beyond said second refractory covering towardsaid second end of said pin and wherein a tubular insulating member isdisposed between said pin and said extending portion of said jacket. 7.An electrical connector according to claim 6 wherein said male memberfurther comprises gasket means disposed circumferentially of saidextending portion of said jacket for sealing between said extendingportion and an instrument.
 8. An electrical connector according to claim1 wherein said female member comprises a resilient, heat-resistantpolymeric inner sheath having a bore for receiving said male member, anelastomeric outer sheath surrounding said inner sheath and having anannular opening aligned with the mouth of said bore, a conductiveelement extending through said sheaths, means disposed in said innersheath for releasably engaging said first end of said pin and meansproviding electrical contact between said pin and said conductiveelement.
 9. An electrical connector according to claim 8 wherein saidjacket has a part snugly receivable in said bore and said opening insaid outer sheath and has an annular ridge extending circumferentiallythereabout and said inner sheath has an internal annular groove in saidbore whereby said ridge snaps into said groove when said male and femalemembers are connected.
 10. An electrical connector according to claim 8wherein said female member further includes a rigid sleeve disposed insaid bore, and said means for releasably engaging said pin and saidmeans providing electrical contact comprises a conductive spring incontact with said conductive element.
 11. An electrical connectoraccording to claim 7 wherein said inner sheath is comprised of afluorocarbon resin.
 12. An electrical connector according to claim 7wherein said conductive element comprises a wire and an inner,insulating heat-resistant polymeric coating is disposed around said wireand an outer protective elastomeric coating is disposed around saidinner coating.
 13. An electricaL connector according to claim 1 whereinsaid pin has a thermal coefficient of expansion compatible with thethermal coefficient of expansion of said refractory coverings.